BEIJING  Two more pairs of panda twins have been born at Chinese breeding centers, the latest in a mini-baby boom for the rare, endangered animals, government media reported Sunday.

Three of the new babies are female and the sex of the fourth is unknown because its mother is still holding it, the Xinhua News Agency reported.

The births bring to four the number of sets of panda twins born last week at Chinese panda-breeding centers.

Panda Xi Mei gave birth to twin cubs Saturday at the Wolong Giant Panda Protection and Research Center near the southwestern city of Chengdu, said Li Desheng, its deputy director. He said another panda, Qian Qian, gave birth to twins Thursday.

"The two mothers and their babies are all well," Li told Xinhua.

The government announced earlier that two female pandas at a breeding center in Chengdu gave birth to twins on Aug. 13 and 14.

China has more than 180 pandas living in captivity, according to the government.

A 2002 government census found there were just 1,596 pandas left in the wild. But Xinhua on Sunday said a new study by Chinese and British scientists has found there might be as many as 3,000.